Since efficient growth methods for C60 molecules, conjugated organic molecules, and the like provide opportunities to design new soft building blocks of which properties are largely different from those observed from powder or solution phase, studies thereon are continuously being progressed.
One approach is to utilize spontaneous precipitation in solution phase that involves self-crystallization of target molecules at liquid-liquid, liquid-air, or liquid-air-solid interfaces, and particularly, crystallization at the liquid-air-solid interface can be achieved by a simple process, called a drop-drying process.
Organic molecules such as C60 molecules, conjugated organic molecules, and the like are readily crystallized by the drop-drying process into 0D, 1D, and 2D nano- to micro-structures at room temperature by simply dissolving them in a solvent and then drop-drying. The drop-drying process has recently attracted much attention due to its simplicity as well as high efficiency in terms of yield and reaction time. However, one important drawback that has not yet been resolved is the controllability of growth direction.
Further, the vertical crystallization of conjugated molecules has been reported only for limited examples (peptides, 1,5-diaminoanthraquinone, copper phthalocyanine). Except for aromatic dipeptide nanotubes that have been vertically grown by the action of a fast evaporating solvent, all other examples require a high temperature, template, or physical vapor transport environment, and thus are not economically efficient and have limited industrial applications.
Accordingly, there is a demand for the development of a method for preparing vertically grown nanostructures of C60 molecules, conjugated molecules, and the like, under mild conditions by a simpler process.